Mars snowflakes are as tiny as red blood cells and made up of carbon dioxide -- not water. (Photo: Creative Commons)

Mars snowflakes are unlike any snowflakes on Earth, researchers report in an upcoming issue of the Journal of Geophysical Research. Mars snowflakes are as tiny as red blood cells and made up of carbon dioxide -- not water.

Researchers analyzed data from two Mars-orbiting spacecrafts, the Mars Global Surveyor (MGS) and the Mars Reconnaissance Orbiter (MRO), and looked at temperature and pressure profiles to determine how and when Mars snowflakes would form.

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"These are very fine particles, not big flakes," Kerri Cahoy, study coauthor and researcher with the Massachusetts Institute of Technology, told Space.com. An astronaut landing during a Martian snowstorm "would probably see it as a fog, because they're so small," she said.

The researchers timed how long laser pulses took to bounce off the Martian surface. Sometimes, the laser would take longer than normal to return, indicating clouds in the atmosphere. By analyzing how much light the clouds reflected, researchers were able to calculate the density of each one.

By putting together all of this data, researchers were able to estimate the size of the individual Mars snowflakes. The size varies from pole to pole, ranging from 8 to 22 microns at the North Pole and 4 to 13 microns at the South Pole. The sizes are microscopic, approximately the size of a human red blood cell, researchers said.

"For the first time, using only spacecraft data, we really revealed this phenomenon on Mars," Renyu Hu, study coauthor and a grad student at MIT told Space.com.

Snowflakes need to form around a kernel, such as a speck of dust, so understanding the size of a Mars snowflake may help researchers better understand how dust plays a role in the Martian atmosphere.

"What kinds of dust do you need to have this kind of condensation?" Hu said. "Do you need tiny dust particles? Do you need a water coating around that dust to facilitate cloud formation?"

In addition, Mars snowflakes could alter heat transport around the red planet.

"They could be completely different in their contribution to the energy budget of the planet," Hu says. "These datasets could be used to study many problems."